Bring a pot of salted water to a boil and boil the cabbage until tender, about 12-15 minutes. Drain off the water and chop the cabbage. Set aside.

Bring another pot of water to a boil and boil the potatoes until tender. Drain off the water and set aside.

Put the leeks in a saucepan, cover with the milk, bring close to boiling and then turn down to a simmer until tender. Set aside.

Add the mace, salt and pepper, and garlic to the pot with the potatoes and mash well with a hand masher. Now add the leeks and their milk and mix in with the potatoes, taking care not to break down the leeks too much. Add a little more milk if necessary to make it smooth. Now mash in the cabbage and lastly the butter. The texture that you want to achieve is smooth-buttery-potato with interesting pieces of leek and cabbage well distributed in it.